Phosphazene polymers have been known for a very long time (H. N. Stokes, Am. Chem. J., 19 782 (1897)). The first such polymer was a polyphosphonitrilic chloride made by heating cyclic phosphonitrilic chloride trimer to a high temperature. In early research, extensive cross-linking occurred leading to the formation of what was referred to as "inorganic rubber". Such polymers were not soluble in any solvent and were of little use. Later research, notably that of Allcock et al., J. Am. Chem. Soc., 87 4216 (1965), lead to the discovery that use of highly purified cyclic phosphonitrilic chloride trimer and closely controlled heating could yield linear phosphonitrilic chlorides (referred to herein as "chloropolymers") that were soluble in solvents such as benzene, toluene, cyclohexane, tetrahydrofuran and the like. Since the linear chloropolymer could be put into solution, this permitted replacement of the chlorine atoms with any of a broad range of organo groups by reaction of the chloropolymer solution with organic compounds which controlled active hydrogen such as amines or alcohols. Frequently the organic compounds were first converted to their alkali metal derivatives whereby alkali metal chloride formed in the reaction with the chloropolymer and the organo groups were bonded to phosphorus. The most common groups bonded to phosphorus were substituted and unsubstituted alkoxides and aryloxides. Typical substituents were alkyl, cycloalkyl, alkoxy, polyalkoxy, alkenyl, halo, haloalkyl, nitro and the like. Representative examples of substituent groups include methoxy, ethoxy, propoxy, butoxy, dodecyloxy, ethoxyethoxy, butoxyethoxy, ethoxyethoxyethoxyethoxy, trifluoroethoxy, trichloroethoxy, 2,2,3,3,4,4,5,5,6,6-decafluorohexoxy, 2-nitroethoxy, cyclohexoxy, phenoxy, naphthoxy, p-ethylphenoxy, o-ethylphenoxy, p-tert-butylphenoxy, p-sec-dodecylphenoxy, allyl, but-3-enoxy, pent-4-enoxy, o-allylphenoxy, o-(but-3-enyl)phenoxy, p-(pent-4-enyl)phenoxy, o-allyl-p-ethylphenoxy, 4-chlorophenoxy, 4-bromophenoxy, 2,4-dichlorophenoxy, 4-trifluoromethylphenoxy, 4-trichloromethylphenoxy, 4-nitrophenoxy, 2,4-dinitrophenoxy, 2,4,6-trinitrophenoxy and the like.
The phosphazene gum that contains the organic substituents has in the past been cured by use of irradiation and free radical initiators. If the substituents contain groups with olefinic unsaturation, the gum could be cured by sulfur vulcanization as used in the rubber industry. These methods all involve special techniques not available in many uses. For example, it is impractical to cure phosphazene-type caulking compounds by use of free radical (e.g. peroxides) or by sulfur vulcanization as both require heating to an elevated temperature under controlled conditions. Thus a need exists for an organophosphazene polymer which will cure merely upon exposure to the atmosphere.